Building a GTIN-14
The first digit is the packaging indicator (1 to 8). Then come the first 12 digits of the unit's EAN-13, without its check digit, and finally a new check digit. For a case of the product 8801234567893, that is 1 + 880123456789 + check digit.
The thick frame around the bars, called bearer bars, protects the code from smearing when printed on cardboard.